1. Field of the Invention
The present invention relates to ink jet printers, and, more particularly, to a method and apparatus for checking the operation of the nozzles in an ink jet printer.
2. Description of the Related Art
Ink jet printhead nozzles are prone to clogging due to dried ink or debris physically impeding the nozzle plate orifice, or due to electrical failure, such as non-functional heater resistors that have failed due to electrostatic discharge, manufacturing defect on the silicon chip, broken TAB bond or chip trace connections, etc.
Even though the printhead ships from the factory with all nozzles testing good, defects including those listed above can occur in shipping, installation, or use of the head. While a head with such a defect is generally still usable, the resultant print quality defects are readily apparent to the user in the form of white lines in the printed pages. This is both a nuisance and a very visible negative contributor to the user's perception of the printer's quality.
Some known printers include a means to sense whether the nozzle/heater resistors read proper resistance. If so, an assumption is made that that nozzle is functioning correctly. Other known printers include a means to print a pattern on the page, each nozzle forming a block or similar pattern in an isolated page position, and moving an optical sensor over the page to sense presence or absence of the printed block or pattern. If a nozzle block is sensed, that nozzle is known to be functional.
Other known printers include means to adjust the printing algorithm so as to account for missing nozzles having been sensed. For instance, a normal print pass might be made, then the paper might be shifted a number of pels, then a second print pass might be made, this time to print the dot positions that were “out” on the first pass.
The drawbacks of the known schemes are that they require fairly expensive circuitry and/or special optical sensors to be used. Also, some require that a test page be printed to determine missing nozzles.
What is needed in the art is a simple, low-cost method and apparatus for performing automatic missing nozzle detection for an ink jet printer.